Cyclic nucleotide-gated ion currents are a large family whose functions range from sensory transduction to pattern generation in members of neural networks. Our broad research objective is to understand the function of one such current, INa,CAMP, in a central nervous system context. In central neurons, Ina,CAMP is regulated in a complex fashion by CAMP, multiple actions of Ca2+, intracellular Ph, and voltage; these factors confer sensitivity to neural activity and shape the current's contributions to neuronal pattern generation. The mollusc Pleurobranchaea provides a well-developed model system of large and well characterized neurons in which Ina,CAMP is expressed in a neuromodulatory framework. These neurons permit straightforward patch and voltage clamp recordings of Ina,CAMP in combination with a variety of experimental manipulations. This proposal describes a plan to elucidate mechanisms of channel regulation and the neuromodulatory context of function. Proceeding from previous work, we are pursuing three specific goals: 1) elucidation of mechanisms of potentiation an inactivation by intracellular Ca2+, current suppression by extracellular Ca2+, and potentiation by H+; 2) probing mechanisms of voltage-dependence of the current; and 3) describing the neuromodulatory context within which Ina, CAMP acts. The first two goals will be approached in studies of inside- out and cell-intact patch recordings of single channel activity, in combination with manipulations of cofactors and inorganic ions. The third goal will be sought in voltage clamp studies of serotonergic neuromodulation of Ina,CAMP using the ion current to report on CAMP metabolism. Ina,CAMP appears to have prominent roles in mediating aspects of behavioral arousal and effects of convulsant drugs. The likely broad distribution of this type of ion current and its combinatorial regulation lends it relevance to many aspects of neural plasticity, pattern generation, and dysfunction in brain.